This invention concerns sensing systems for determining one or more positions of a moving element, for example a piston movably disposed inside a cylinder.
More specifically, the present invention concerns magnetic and inductive sensors which are mounted on the housing of a working cylinder arrangement. Such sensors have been successfully employed for touchlessly determining the exact position of a pneumatic or hydraulic piston that is movable inside a working cylinder. For this, guide grooves are arranged on the exterior of the housing. Axially movable magnetic field sensors are placed in the grooves, and following adjustment they can be fixed in the guide groove at a desired position, as is described, for example, in published German patent applications DE 196 43 413 A1 and DE 196 53 222 A1. A sensor positioned and secured in this manner generates switching signals in dependency on the position of the piston. Several sensing positions arranged over the length of the stroke of the piston in the cylinder are often needed. Most frequently, the fully retracted and extended, terminal positions of the pistons must be determined. For each sensing position a sensor is necessary, so that for sensing the terminal positions two sensors are needed. The necessary two sensors are usually secured in the same groove. Since each sensor requires its own electrical connections for supplying voltage and current, signal conductors and hydraulic lines, a relatively large bundle of lines and conductors are required for just one working cylinder. If many working, e.g. pneumatic, cylinders are installed in a small space, as required, for example, by robotic grippers and small manipulating devices, serious space problems are encountered because of the large number of lines and conductors that must be accommodated. The problem is exacerbated when additional piston positions over and above the terminal positions must be monitored with a corresponding number of additional sensors.